Manufacturing method of silicon wafer

ABSTRACT

An active layer side silicon wafer is heat-treated in an oxidizing atmosphere to thereby form a buried oxide film therein. The active layer side silicon wafer is then bonded to a supporting side wafer with said buried oxide film interposed therebetween thus to fabricate an SOI wafer. Said oxidizing heat treatment is carried out under a condition satisfying the following formula: 
 
[ Oi ]≦2.123×10 21 exp(−1.035/ k ( T +273)), 
 
where, T is a temperature of the heat treatment, and [Oi] (atmos/cm 3 ) is an interstitial oxygen concentration.

FIELD OF THE INVENTION

The present invention relates to a manufacturing method of a siliconwafer, specifically to a manufacturing method of a silicon wafer withreduced COP and also to a manufacturing method of a SOI wafer using thesame silicon wafer.

PRIOR ART

In general, a single crystal of silicon, which has grown with theCzochralski method (i.e., the CZ method), contains defects, each havinga size of about 0.1 μm to 0.3 μm, in a density of 1×10⁵/cm³ to 1×10⁷/cm³even in the condition just after its having been grown (in the as-grownstate). Such a defect is identified as a minute void generated by anaggregation of excess vacancy during cooling of the silicon singlecrystal. As it is, when a silicon wafer that has been sliced from thatsilicon single crystal is polished, those minute voids would comeexposed as turning out to be pits in a surface of the silicon wafer.Those pits and other voids existing in the vicinity of the surface couldbe obstacles in a fine device structure. Those defects are referred toas COP (Crystal Originated Particle).

There are known methods for reducing the COP in the silicon wafer,including, for example, a method disclosed in the Japanese PatentLaid-open Publication No. Hei9-22993, in which a heat treatment isapplied to a silicon wafer in a reducing atmosphere by hydrogen and thelike or in an inert atmosphere by argon and the like.

Another method has been known, as disclosed in the Japanese PatentPublication No. 3085184, in which an epitaxial wafer is used for asilicon wafer in an active layer side (hereafter, referred to as anactive layer side silicon wafer) of a SOI wafer.

In yet another known method, as disclosed in the Japanese PatentLaid-open publication No. Hei8-330316, during growing of a siliconsingle crystal, a ratio of its growing rate V to a temperature gradientG in the single crystal defined along a growing direction of the siliconsingle crystal, or V/G, is controlled appropriately to thereby allow thegrowing of the silicon single crystal containing no COP.

The method for applying the heat treatment in the hydrogen or argonatmosphere has been found effective to vanish the COP existing in aregion defined by a depth less than some μm from the surface of thesilicon wafer. This method, however, has not worked effectively tovanish the COP existing in a region defined by the depth more than someμm from the surface of the silicon wafer.

In the method using the epitaxial wafer for the active layer sidesilicon wafer, it is true that the SOI wafer having an active layercontaining no COP can be manufactured because of no COP existing in theepitaxial wafer, but it is impossible to manufacture the SOI waferhaving the active layer containing no defect since the epitaxial wafercontains other defects inherent to it, such as stacking fault and/ordislocation. Further disadvantageously, from the fact that the epitaxialwafer is rather expensive, using the epitaxial wafer for the activelayer side silicon wafer of the SOI wafer could increase themanufacturing cost of the SOI wafer.

Further, properly controlling the V/G allows the silicon single crystalcontaining a region having no COP to be grown. However, if the V/Gexceeds an upper allowable limit, an OSF-ring region (i.e., a regionexhibiting a ring shape of Oxidation induced Stacking Fault generated bythe heat treatment) or a COP region would appear, and if the V/G fallsout of a lower allowable limit, a dislocation cluster region wouldappear. The allowable range of the V/G is quite narrow, and accordinglyit is not easy to produce such crystal containing no COP and OSF-ringregions and no dislocation cluster in a stable manner.

An object of the present invention is to provide a manufacturing methodof a silicon wafer, which can vanish the COP within the silicon wafer.Especially, the object of the present invention is to provide amanufacturing method of a silicon wafer, which can vanish the COPexisting in a region defined by a depth more than some μm from thesurface of the silicon wafer.

Another object of the present invention is to provide a manufacturingmethod of a SOI wafer for manufacturing a silicon wafer containing noCOP existing therein, as well as for manufacturing a SOI wafer by usingsaid silicon wafer as an active layer side silicon wafer.

Yet another object of the present invention is to provide amanufacturing method of a SOI wafer, which can reduce the COP within theactive layer side silicon wafer, without using an expensive epitaxialwafer or a no-defect crystal, which cannot be manufactured easily, orwithout the need for introducing any additional new steps to theexisting SOI manufacturing process.

DISCLOSURE OF THE INVENTION

A first invention provides a manufacturing method of a silicon wafer, inwhich a silicon wafer that has been sliced from a silicon single crystalis heat-treated in an oxidizing atmosphere, wherein

-   -   assuming that a temperature at which said heat treatment is        carried out in said oxidizing atmosphere is denoted as T (° C.)        and an interstitial oxygen concentration is denoted as [Oi]        (atoms/cm³), said manufacturing method of the silicon wafer        characterized in that a relation between said temperature T and        said interstitial oxygen concentration [Oi] may satisfy the        following formula:        [Oi]≦2.123×10²¹exp(−1.035/k(T+273)),        where, said interstitial oxygen concentration is a value        measured in accordance with FT-IR method (ASTM F-121, 1979) and        the k is the Boltzmann's constant, 8.617×10⁻⁵(eV/K).

In this first invention, the silicon wafer is heat-treated in theoxidizing atmosphere. During this treatment, the temperature T and theinterstitial oxygen concentration [Oi] satisfies the relation defined bythe above formula. Resultantly, the COP within the silicon wafer can bevanished.

If the silicon wafer is heat-treated in the argon or hydrogenatmosphere, the COP in the silicon wafer existing in the region close tothe surface will vanish. The COP in the deeper region, however, will notvanish. In contrast to this, the heat treatment in the oxidizingatmosphere, as described above, can vanish the COP even in the deeperregion within the silicon wafer. The reason for this is thatinterstitial silicon atoms generated in the surface of the silicon waferby the oxidizing heat treatment are diffused into the internal of thesilicon wafer and that thus diffused atoms fill the COP representing thevoid.

It is to be noted that the atmosphere used in the above heat treatmentshould not necessarily be the atmosphere of 100% oxygen, but it may bethe atmosphere containing the oxygen partially.

A second invention provides a manufacturing method of a silicon wafer inaccordance with the first invention, in which the silicon single crystalhas been doped with phosphorus by a neutron irradiation.

In the manufacturing method of the silicon wafer according to the secondinvention, firstly the silicon single crystal bar is grown withoutdoping with any dopant.

The neutrons are then irradiated to thus grown silicon single crystalbar to thereby dope the silicon single crystal bar with the phosphorus.This can make a specific resistance in the silicon single crystaluniform, especially along its growing axis.

A third invention provides a manufacturing method of a silicon wafer inaccordance with the first or the second invention, in which said siliconsingle crystal has been doped with nitrogen by a concentration of 2×10¹³atoms/cm³ or more.

In the manufacturing method of the silicon wafer according to the thirdinvention, the silicon single crystal has been doped with nitrogen by aconcentration of 2×10¹³ atoms/cm³ or more. This can help reduce the COPsize in the as-grown crystal, and facilitates the vanishment of the COPin the shorter period of heat treatment. The reason why the COP size canbe reduced by the doping with nitrogen is that the doping with thenitrogen can suppress the aggregation of vacancies in the course ofcooling during the crystal growing.

Further, the pinning effect for the dislocation by the nitrogen cansuppress the generation of the slip dislocation possibly caused by thehigh temperature heat treatment.

Concerning the above, with the doping amount of the nitrogen less than2×10¹³ atoms/cm³, the above pointed effect could not be achieved.

Any doping method of nitrogen may be employed, that has been known inthe art. For example, a silicon wafer coated with a nitrogen film may befused together with a silicon polycrystal material to thereby accomplishthe doping.

A fourth invention provides a manufacturing method of a silicon wafer inaccordance with any one of the first to third inventions, in which saidsilicon single crystal has been doped with carbon by a concentration of5×10¹⁶ atoms/cm³ or higher.

In the manufacturing method of the silicon wafer according to the fourthinvention, the silicon single crystal has been doped with the carbon ina density of 5×10¹⁶ atoms/cm³ or more. This can improve the mechanicalstrength of the silicon wafer and suppress the slip otherwise induced inthe heat treatment, as it is the case with the nitrogen doping.

The doping method of the carbon is not specifically limited, and forexample, a predetermined amount of carbons may be fused together with asilicon polycrystal material to thereby accomplish the doping.

A fifth invention provides a manufacturing method of a silicon wafer inaccordance with any one of the first to the fourth inventions, in whichthe silicon wafer is mirror-polished after said heat treatment in saidoxidizing atmosphere. The surface state of the silicon wafer prior tothe heat treatment may be a state with no mirror polishing appliedthereto (or etched state).

If the silicon wafer is heat-treated in the oxidizing atmosphere, theCOP in the region defined by a depth of about 5 μm or more from thesurface of the silicon wafer vanishes. On the other hand, there remainsthe COP in a shallow region defined by the depth of 5 μm or less fromthe surface of the silicon wafer, in a concentration level of about 1/10to 1/100 relative to that prior to the heat treatment in the oxidizingatmosphere. To address this, the surface of the silicon wafer ismirror-polished after the heat treatment in the oxidizing atmosphere.Since the polishing is carried out after the heat treatment, no mirrorpolishing is necessary to be carried out prior to the heat treatment.That is, the polishing after the heat treatment is performed for the twopurposes of: flattening the surface; and removing the remaining COP inthe vicinity of the surface. Different from the wafer that has beenheat-treated in the non-oxidizing atmosphere by the hydrogen or argon,there is no need to limit the polishing amount to a specific value fromthe reason that if the wafer having the interstitial oxygenconcentration satisfying the condition defined by the present inventionis heat-treated in the oxidizing atmosphere, the COP in the deep regioncan be vanished, and accordingly the polishing after the heat treatmentwould not expose the COP, which could otherwise form the pit.

A sixth invention provides a manufacturing method of a SOI wafer, inwhich a SOI wafer is manufactured by using a silicon wafer manufacturedby the method as defined by the fifth invention for an active layer sidewafer.

A seventh invention provides a manufacturing method of a SOI wafer, inwhich a buried oxide film is formed by applying a heat treatment to anactive layer side silicon wafer in an oxidizing atmosphere, and saidactive layer side silicon wafer is then bonded with a wafer in asupporting side (hereafter, referred to as a supporting side wafer) withsaid buried oxide film interposed therebetween thus to manufacture abonded SOI wafer, wherein

-   -   assuming that a temperature at which said heat treatment is        applied to said active layer side silicon wafer in said        oxidizing atmosphere is denoted as T (° C.) and an interstitial        oxygen concentration of said active layer side silicon wafer is        denoted as [Oi] (atoms/cm³), said manufacturing method of the        SOI wafer characterized in that a relation between said heat        treatment temperature T and said interstitial oxygen        concentration [Oi] of said active layer side silicon wafer may        satisfy the following formula:        [Oi]≦2.123×10²¹exp(−1.035/k(T+273)),        where, said interstitial oxygen concentration is a value        measured in accordance with FT-IR method (ASTM F-121, 1979) and        the k is the Boltzmann's constant, 8.617×10⁻⁵ (eV/K).

In the manufacturing method of the SOI wafer according to the seventhinvention, the heat treatment to be applied to the active layer sidesilicon wafer for forming the buried oxide film therein is carried outunder the condition where the relation between the temperature of thatheat treatment and the interstitial oxygen concentration in the wafersatisfies the above formula. Resultantly, the buried oxide film isformed in the surface of the active layer side silicon wafer, while theCOP can be reduced. By bonding thus fabricated active layer side waferwith the supporting side wafer, the bonded SOI wafer with the reducedCOP can be fabricated. In this regard, advantageously the presentinvention is characterized in that the SOI wafer having the SOI layerwith reduced COP can be manufactured without introducing any additionalsteps to the typical manufacturing process of the bonded SOI wafer.

An eighth invention provides a manufacturing method of a SOI wafer inaccordance with the seventh invention, in which a wafer fabricated froma silicon single crystal doped with phosphorus by a neutron irradiationis used as said active layer side silicon wafer.

The silicon wafer that has been sliced out of the silicon single crystaldoped with the phosphorus by the neutron irradiation is used for theactive layer side silicon wafer, to which said oxidizing heat treatmentis applied. Further, the active layer side silicon wafer is bonded withthe supporting side wafer with the buried oxide film interposedtherebetween. Resultantly, the SOI wafer having the SOI layer withreduced COP can be fabricated. In this regard, a variation in thespecific resistance of the active layer side silicon wafers, which havebeen sliced out of the same single crystal, is limited to an extremelysmall range, and so such SOI wafers can be fabricated that have uniformspecific resistance.

A ninth invention provides a manufacturing method of a SOI wafer inaccordance with the seventh or the eighth invention, in which saidactive layer side silicon wafer is fabricated by using a silicon singlecrystal doped with nitrogen by a concentration of 2×10¹³ atoms/cm³ ormore.

Advantageously, in said active layer side silicon wafer, a mechanicalstrength can be improved as compared to that of the silicon wafer withno-nitrogen doped, and also the occurrence of slipping in the heattreatment can be prevented. Furthermore, the COP size can be reduced, sothat the COP can be vanished in much shorter time during the oxidizingheat treatment.

A tenth invention provides a manufacturing method of a SOI wafer inaccordance with any one of the seventh to the ninth invention, in whichsaid active layer side silicon wafer is fabricated by using a siliconsingle crystal doped with carbon by a concentration of 5×10¹⁶ atoms/cm³or more.

The doping with carbon improves the mechanical strength of the wafer ascompared with the non-doped products and prevents the occurrence ofslipping.

An eleventh invention provides a manufacturing method of a SOI wafer, inwhich an active layer side silicon wafer is bonded to a supporting sidewafer with an insulating film interposed therebetween and then a heattreatment for enhancing a bonding strength is applied to thus bondedwafer in an oxidizing atmosphere to thereby manufacture a bonded SOIwafer, wherein

-   -   assuming that a temperature at which said heat treatment for        enhancing the bonding strength is carried out in said oxidizing        atmosphere is denoted as T (° C.) and an interstitial oxygen        concentration of said active layer side silicon wafer is denoted        as [Oi] (atoms/cm³), said manufacturing method of the SOI wafer        characterized in that a relation between said temperature T and        said interstitial oxygen concentration [Oi] may satisfy the        following formula:        [Oi]≦2.123×10²¹exp(−1.035/k(T+273)),        where, said interstitial oxygen concentration is a value        measured in accordance with FT-IR method (ASTM F-121, 1979) and        the k is the Boltzmann's constant, 8.617×10⁻⁵(eV/K).

In the manufacturing method of the SOI wafer according to the eleventhinvention, after the active layer side silicon wafer having been bondedto the supporting side wafer, thus bonded wafer is applied with the heattreatment for enhancing the bonding strength in the oxidizing atmospherewhich satisfies the above condition for the temperature and the oxygenconcentration. This allows for the production of the SOI wafer with thereduced COP in the active layer (SOI layer) without adding any new stepsto the typical manufacturing process of the bonded SOI wafer.

A twelfth invention provides a manufacturing method of a SOI wafer inaccordance with the eleventh invention, in which the SOI wafer isfabricated by using said active layer side silicon wafer made from thesilicon single crystal doped with phosphorus by the neutron irradiation.

Owing to the phosphorus doping by the neutron irradiation, the siliconsingle crystal bar may have a uniform dopant concentration, or a uniformspecific resistance, even in a crystal growing axis direction.Accordingly, the silicon wafers fabricated from the same single crystalbar may exhibit the uniform specific resistance.

A thirteenth invention provides a manufacturing method of a SOI wafer inaccordance with the eleventh or the twelfth invention, in which saidactive layer side silicon wafer is fabricated by using the siliconsingle crystal doped with nitrogen by a concentration of 2×10¹³atoms/cm³ or more.

The doping with nitrogen improves the mechanical strength of the activelayer side silicon wafer, prevents the occurrence of the slipping andallows the COP to vanish in a short time.

A fourteenth invention provides a manufacturing method of a SOI wafer inaccordance with any one of the eleventh to the thirteenth invention, inwhich said active layer side silicon wafer is fabricated by using thesilicon single crystal doped with carbon by a concentration of 5×10¹⁶atoms/cm³ or more.

The doping with carbon to a predetermined concentration improves themechanical strength of the active layer side silicon wafer and preventsthe occurrence of slipping.

A fifteenth invention provides a manufacturing method of a SOI wafer,comprising the steps of:

-   -   fabricating an active layer side silicon wafer by firstly        applying an oxidizing heat treatment to a silicon wafer, which        satisfies the following formula representing a relation between        a heat treatment temperature T and an interstitial oxygen        concentration [Oi]:        [Oi]≦2.123×10²¹exp(−1.035/k(T+273)),        where, T(° C.) is the temperature at which said heat treatment        is carried out in an oxidizing atmosphere, and [Oi] (atoms/cm³)        is the interstitial oxygen concentration in the silicon wafer,        wherein said interstitial oxygen concentration is a value        measured in accordance with FT-IR method (ASTM F-121, 1979) and        the k is the Boltzmann's constant, 8.617×10 ⁻⁵(eV/K), and by        secondly removing an oxide film and applying a mirror-polishing;    -   forming an ion implanted layer in said active layer side silicon        wafer by forming an oxide film on said active layer side silicon        wafer, and ion-implanting via said oxide film;    -   subsequently, forming a bonded wafer by bonding said active        layer side silicon wafer to a supporting side wafer with said        oxide film interposed therebetween; and    -   then, separating a part of said active layer side silicon wafer        from a boundary defined by said ion implanted layer by holding        said bonded wafer at a predetermined temperature to thereby        apply a heat treatment thereto.

In the manufacturing method of the SOI wafer according to the fifteenthinvention, after applying such oxidizing heat treatment to the siliconwafer that satisfies the above condition, the oxide film is removedtherefrom and the mirror polishing is applied thereto thus to fabricatethe COP-free wafer. In the fabrication of this COP-free wafer, since thepolishing is applied after the heat treatment, there is no need forapplying the mirror-polishing prior to the heat treatment. That is, thepolishing after the heat treatment is carried out for two purposes of:flattening the surface; and removing the COP remaining in the vicinityof the surface. Thus fabricated silicon wafer is employed as the activeside silicon wafer to manufacture the SOI wafer by the typical smart-cutprocess. That is, the oxide film is formed on the active layer sidesilicon wafer, and the ions are implanted via said oxide film. Further,the active layer side silicon wafer is bonded to the supporting sidewafer with the oxide film interposed therebetween, and a part of theactive layer side silicon wafer is separated from the boundary definedby the ion-implanted layer through the heat treatment for separation tothereby fabricate the SOI wafer. This allows for the manufacturing ofthe SOI wafer containing no COP in the SOI layer.

A sixteenth invention provides a manufacturing method of a SOI wafer inaccordance with the fifteenth invention, in which a surface of theseparated active layer side wafer (donor wafer) is mirror-polished sothat it can be used repeatedly as a substrate for forming a new activelayer of the SOI wafer.

A seventeenth invention provides a manufacturing method of a SOI waferin accordance with the fifteenth or the sixteenth invention, in whichsaid active layer side silicon wafer is fabricated by using a siliconsingle crystal doped with phosphorus by neutron irradiation.

The doping with phosphorus by the neutron irradiation allows a siliconsingle crystal bar to obtain a uniform specific resistance in thecrystal growing axis direction thereof.

An eighteenth invention provides a manufacturing method of a SOI waferin accordance with any one of the fifteenth to the seventeenthinvention, in which said active layer side silicon wafer is fabricatedby using a silicon single crystal doped with nitrogen by a concentrationof 2×10¹³ atoms/cm³ or more.

The doping with nitrogen improves the mechanical strength, prevents theoccurrence of slipping and allows the COP to vanish in a short time.

A nineteenth invention provides a manufacturing method of a SOI wafer inaccordance with any one of the fifteenth to the eighteenth invention, inwhich said active layer side silicon wafer is fabricated by using asilicon single crystal doped with carbon by a concentration of 5×10¹⁶atoms/cm³ or more.

The doping with carbon in a predetermined concentration improves themechanical strength of the active layer side silicon wafer and reducesthe occurrence of the slipping.

As described above, according to the present invention, the COP existingin the deeper region of the silicon wafer can be vanished as comparedwith the case where the silicon wafer is heat-treated in the argon orthe hydrogen atmosphere to vanish the COP therein.

Further, in the present invention, the active layer side silicon wafercan be fabricated without using expensive epitaxial wafer therebyreducing the manufacturing cost of the SOI wafer.

Furthermore, the present invention allows for the manufacturing of theSOI wafer without the need for any special steps for vanishing the COPin the active layer side silicon wafer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 presents a result from an investigation on a condition forvanishing the COP by an oxidizing heat treatment according to thepresent invention, indicating that the COP vanishes in a region belowthe broken line.

PREFERRED EMBODIMENTS FOR IMPLEMENTING THE PRESENT INVENTION

First of all, there will be described an experiment that has beenconducted in order to find a boundary condition for vanishing the COP inthe oxidizing heat treatment according to the present invention.

A plurality of silicon wafers were prepared, which have differentinterstitial oxygen concentrations from one another. Those siliconwafers were placed in either of an oxygen atmosphere, a nitrogenatmosphere, a hydrogen atmosphere or an argon atmosphere, where the heattreatment was applied thereto at respectively varied temperature. Then,each of the silicon wafers was inspected for the existence of the COP ina region defined by a depth of 300 μm from the surface. The oxygenconcentration was measured in accordance with the FT-IR method (thescaling factor: ASTM F-121, 1979). Further, whether or not the COP isexisting was determined based on the result of measurements by theinfrared bright field interference method. An evaluation of the defectwithin the silicon wafers by the infrared bright-field interferencemethod was conducted by using the OPP (Optical Precipitate Profiler)available from Accent Optical Technologies. It is to be noted that theevaluation of the defect by the OPP was carried out by using a samplesilicon wafer with its both front and back surfaces mirror-polished andthe lower limit of detection size of about 30 nm in order to avoid theeffect from the uneven front and back surfaces of the silicon wafers. Inthe inspection, when the defect density had reached the level equal toor less than 1.1×10⁴/cm³, it was determined that the COP had vanished.

The result from the investigation is shown in the below Table 1. It isto be noted that Table 1 indicates a critical temperature (the lowesttemperature) at which the COP vanishes in each wafer with differentoxygen concentration. TABLE 1 [Oi] (atoms/cm³) Temperature T (° C.)1/(k(T + 273)) (1/eV) 3.020E+17 1087 8.533 3.766E+17 1113 8.3735.191E+17 1175 8.014 5.816E+17 1188 7.943 6.005E+17 1200 7.878

The values shown in Table 1 represent the result from the heat treatmentthat was conducted in the oxygen atmosphere. The heat treatmentsconducted respectively in the nitrogen, the hydrogen and the argonatmosphere could not succeed in vanishing the COP in the depth of 300μm.

It can be seen from the result of Table 1 that if the oxygenconcentration in the silicon wafer is low, then the COP can be vanishedat a low temperature. By representing this relation in the Arrheniusplot, as shown in FIG. 1, it is found that the conditions for vanishingthe COP in the silicon wafer by the heat treatment in the oxidizingatmosphere may be expressed by the following formula:[Oi]≦2.123×10²¹exp(−1.035/k(T+273))  (1)where, the interstitial oxygen concentration [Oi] is represented by avalue measured in accordance with the FT-IR method (ASTM F-121, 1979)and the k represents the Boltzmann's constant, 8.617×10⁻⁵(eV/K).

Preferred embodiments of the present invention will now be described,which is made only for the illustration but not intended to limit thescope of the present invention.

For the COP evaluation within the wafer in the illustrated embodiment,the OPP (the detection size of 30 nm) from Accent Optical Technologieswas employed similarly to the experiment for finding the COP vanishingcondition. The defect evaluation in the wafer surface in the illustratedembodiment was carried out in the light scattering method. In specific,the Surfscan 6220 (the lower limit of detection size of 0.105 μm) or theSurfscan SP1 (the lower limit of detection size of 0.85 μm) manufacturedfrom KLA Tencor were used.

The heat treatment in the oxidizing atmosphere applied to the siliconwafers having different interstitial oxygen concentrations will now bedescribed.

After a 6-inch mirror-polished wafer having an interstitial oxygenconcentration of 4.0×10¹⁷ atoms/cm³ had been applied with the heattreatment in the oxygen atmosphere at 1150° C. for two hours, the oxidefilm was removed therefrom to thus prepare a sample A. It is to be notedthat when the temperature of the heat treatment is 1150° C., theinterstitial oxygen concentration satisfying the relation defined by theformula (1) is 4.55×10¹⁷ atoms/cm³ or less. Accordingly, the sample A isa wafer that has been applied with the heat treatment that satisfies theformula (1).

On one hand, a wafer having the interstitial oxygen concentration of5.5×10¹⁷ atoms/cm³ was processed similarly and thus a sample B wasfabricated. This sample B has not been applied with the heat treatmentsatisfying the relation of the formula (1).

Then, the samples A and B were inspected for the defect by using the OPPto measure the defect density at a location defined by the depth of 300μm, and it was found that no defect was detected in the sample Aindicating the defect density not greater than 1.1×10⁴ defects/cm³,while the defects were detected in the sample B with the defect densityof about 4.4×10⁶ defects/cm³. By performing the heat treatmentsatisfying the relation defined by the formula (1), such a silicon wafercan be successfully fabricated that has an extremely low defect densityin the deep location, which has not been achieved by the heat treatmentin the hydrogen or argon atmosphere according to the prior art.

The case where the silicon single crystal is doped with phosphorus bythe neutron irradiation will now be described.

A 400 mm long ingot was sliced out of an 8-inch silicon single crystal,that had grown in the CZ method without being doped with any dopant andhad the interstitial oxygen concentration in a range of 4.5 to 6.0×10¹⁷atmos/cm³, and thus obtained ingot was doped with phosphorus by applyingthe neutron irradiation thus to fabricate the ingot having a specificresistance of about 50Ω·cm. The specific resistances (by Ω·cm) beforeand after the neutron irradiation are shown in Table 2. Those alphabets,p and n, placed in front of the numeric values represent p-type andn-type, respectively. It can be seen from the result in Table 2 that ifdoped with phosphor by the neutron irradiation, the silicon ingotexhibits more uniform specific resistances in respective locations.TABLE 2 Upper end of ingot Lower end of ingot Center 50 mm 90 mm Center50 mm 90 mm of from from of from from crystal center center crystalcenter center Before p-7869 p-7791 p-7771 p-7347 p-6840 p-7423 neutronirradiation After n-4.73 n-4.89 n-4.85 n-4.94 n-5.00 n-4.95 neutronirradiation

Then, a wafer having the oxygen concentration of 5.5×10¹⁷ atoms/cm³ wassliced out of said ingot, and the wafer was mirror-polished and thenapplied with the heat treatment in the oxygen atmosphere at 1200° C. for2 hours. At the temperature of 1200° C. in the heat treatment, theinterstitial oxygen concentration satisfying the formula (1) is6.06×10¹⁷ atoms/cm³ or less. Therefore, the above oxygen concentrationsatisfies the formula (1). Then, the COP density at the location definedby the depth of 300 μm from the surface of the silicon wafer wasmeasured with the OPP. As it is, the COP was not detected, and the COPdensity at that time was confirmed to be 1.1×10⁴ counts/cm³ or less.

Further, the sample having the same level as that evaluated with the OPPwas measured with the SP1, and it was found that the number of defectsin the surface was 180 counts. In this concern, from the fact that thenumber of defects before the heat treatment in the oxygen atmosphere wasabout 2560, it was found that the number of defects had been reduceddown to 1/10 or less. After the wafer surface having been again polishedby about 5 μm, the defects in the surface were measured again with theSP1, and no defect was detected. This implies that the defects remainonly in the shallow region defined by the depth of 5 μm or less, or inthe vicinity of the surface. The reason why the COP in the vicinity ofthe surface remains unvanished is that the oxygen in the atmosphere isdiffused internally in the wafer during the oxidizing heat treatment,and thereby the oxygen concentration in the vicinity of the surface isno more satisfying the relation defined by the formula (1). In thisviewpoint, the following experiment was conducted.

A wafer having the oxygen concentration of 5.2×10¹⁷ atoms/cm³ was slicedout of said ingot and applied with the etching in order to remove anystrain caused by the processing, and to thus obtained wafer in the stateprior to the mirror-polishing, the heat treatment was applied in theoxygen atmosphere at 1200° C. for two hours. After that, the oxide filmwas removed, and the mirror-polishing was applied to the wafer by about10 μm thick. The surface of thus fabricated wafer was measured with theSP1, and no defect was detected. This means that in the case where theheat treatment in the oxygen atmosphere is applied first and then themirror-polishing is carried out, there is no need for performing themirror-polishing before the heat treatment in the oxygen atmosphere.That is, mirror-polishing process after the heat treatment in the oxygenatmosphere is serving both for removing the layer of remaining defectsand for flattening the surface.

Then the case where a silicon single crystal is doped with nitrogen willnow be described.

An embodiment of a wafer doped with nitrogen will be described first. A6-inch wafer having the interstitial oxygen concentration of 5.6×10¹⁷atoms/cm³ and the nitrogen concentration of 2×10¹³ atoms/cm³ was appliedwith the heat treatment in the oxygen atmosphere at 1200° C. for 0.5hour thus to prepare a sample C.

Besides, a wafer having the interstitial oxygen concentration of5.1×10¹⁷ atoms/cm³ and having not doped with nitrogen was processedsimilarly thus to prepare a sample D.

In addition, a wafer that had been sliced out of the same crystal as thesample D was processed in the same manner as the sample D, except thatthe heat treatment was carried out at 1200° C. for 1 hour, and thus asample E was prepared.

The defect density for each of those three samples was evaluated withthe OPP. The results indicate that no defect was detected for thesamples C and E, with the defect density of 1.1×10⁴ counts/cm³ or less.However, the defect identified by 2.2×10⁵ counts/cm³ was detected in thesample D. Further, in the inspection for the occurrences of the slippingdislocation by the X-ray topography, about 1 cm long slippingdislocation was observed for the samples D and E, while no slippingdislocation was observed in the sample C that had been doped withnitrogen.

It was found that by doping with the nitrogen, advantageously the timerequired for vanishing the COP was reduced and further the mechanicalstrength of the wafer was improved and the occurrence of the slippingdislocation was prevented. However, said two effects were not observedin the case of nitrogen concentration lower than 2×10¹³ atmos/cm³.

The case where the silicon single crystal is doped with carbon will nowbe described.

Firstly, a 6-inch wafer having the interstitial oxygen concentration of4.1×10¹⁷ atoms/cm³ and the carbon concentration of 5×10¹⁶ atoms/cm³ wasapplied with the heat treatment in the oxygen atmosphere at 1150° C. fortwo hours thus to prepare a sample F. A wafer having the interstitialoxygen concentration of 3.9×10¹⁷ atoms/cm³ and having not been dopedwith carbon was similarly processed thus to prepare a sample G.

The result from the evaluation of defect density with the OPP indicatesthat no defect was detected for the samples F and G, with the defectdensity of 1.1×10⁴ counts/cm³ or less. In the inspection for theoccurrences of the slipping dislocation by the X-ray topography, about 4mm long slipping dislocation was observed for the sample G, while noslipping dislocation was observed in the sample F that had been dopedwith carbon.

It was found that the doping with the nitrogen improved the mechanicalstrength of the wafer and could prevent the occurrence of the slippingdislocation. However, this effect was not observed in the case of thecarbon concentration lower than 5.0×10¹⁶ atoms/cm³.

The COP vanishment during the formation of the buried oxide film in theSOI wafer will now be described.

First of all, a wafer was sliced out of a 6-inch silicon single crystalhaving the interstitial oxygen concentration of 4.9×10¹⁷ atoms/cm³ andthe nitrogen concentration of 7×10¹³ atoms/cm³, and mirror-polished, andthus obtained wafer was used as the active layer side wafer and appliedwith the heat treatment for forming the buried oxide film at 1175° C.for 2 hours. The heat treatment for bonding with the supporting sidewafer was performed at 1150° C. for 2 hours, and thus obtained bondedwafer was mirror-polished until the thickness of the active layerreached 10 μm, thus fabricating the SOI wafer.

It is to be noted that the interstitial oxygen concentration satisfyingthe formula (1) at the temperature of 1175° C. is 5.26×10¹⁷ atoms/cm³ orless. Therefore, the relation between the temperature during theformation of the buried oxide film and said oxygen concentrationsatisfies the formula (1).

The surface of the active layer of the bonded SOI wafer that had beenfabricated in the above described manufacturing method was evaluated byusing the Surfscan 6220, and no defect was detected. This means that bycontrolling the interstitial oxygen concentration of the active layerside wafer and the temperature of the heat treatment for forming theburied oxide film so as to satisfy the relation defined by the formula(1), the high quality SOI wafer containing no COP could be successfullyfabricated without adding any new steps to the existing manufacturingmethod of the typical bonded SOI wafer.

The COP vanishment in the bonded SOI wafer during the heat treatment forenhancing the bonding strength will now be described.

First of all, the heat treatment (at 1050° C. for 4 hours) for formingthe buried oxide film was applied to the supporting side wafer.Secondly, a 6-inch wafer having the interstitial oxygen concentration of3.7×10¹⁷ atoms/cm³ and the nitrogen concentration of 8×10¹³ atoms/cm³and also having been finished with the mirror-polishing was used as theactive layer side wafer, and the heat treatment for bonding it with saidsupporting side wafer containing the oxide film was applied at 1150° C.for 2 hours and then the polishing is applied to thus obtained bondedwafer until the thickness of the active layer reached 10 μm, thusfabricating the SOI wafer. The relation between the temperature 1150° C.of the heat treatment for enhancing the bonding strength and saidinterstitial oxygen concentration satisfies the formula (1).

The surface of the active layer of the bonded SOI wafer havingfabricated according to the above-described method was evaluated withthe Surfscan 6220, and no defect was detected. This means that bycontrolling the interstitial oxygen concentration of the active layerside wafer and the temperature of the bonding heat treatment so as tosatisfy the relation defined by the formula (1), the high quality SOIwafer containing no COP could be successfully fabricated without addingany new steps to the existing manufacturing method of the typical bondedSOI wafer.

The SOI wafer having a thinned active layer will now be described.

First of all, a wafer having the interstitial oxygen concentration of3.8×10¹⁷ atoms/cm³ and the nitrogen concentration of 9×10¹³ atoms/cm³was sliced out of a 6-inch silicon single crystal, applied with theetching in order to remove the strain caused by the processing and then,in the state prior to the mirror-polishing, applied with the heattreatment in the oxygen atmosphere at 1150° C. for 2 hours. The relationbetween the temperature of this heat treatment and said interstitialoxygen concentration satisfies the formula (1). After that, the oxidefilm was removed, and the mirror-polishing was performed by about 10 μmthick. Thus processed wafer was used as the active layer side wafer, andthe heat treatment for bonding it with the supporting side wafercontaining the buried oxide film was performed at 1150° C. for 2 hours,and the polishing was applied until the thickness of the active layerreached 1 μm, thus fabricating the SOI wafer.

The active layer of this SOI wafer was inspected to evaluate the defectin its surface, and no defect was detected. This means that by employingas the active layer side wafer the wafer that had been applied with theheat treatment satisfying the condition defined by the formula (1) andthen finished by the mirror-polishing, the SOI wafer containing no COPeven with the thinned active layer could be successfully fabricated.

Finally, a method for manufacturing the SOI wafer by using the smart cutmethod will be described.

Firstly, a wafer having the interstitial oxygen concentration of4.0×10¹⁷ atoms/cm³ and the nitrogen concentration of 8×10¹³ atoms/cm³was sliced out of an 8-inch silicon single crystal, applied with theetching in order to remove the strain caused by the processing and then,in the state prior to the mirror-polishing, applied with the heattreatment in the oxygen atmosphere at 1150° C. for 2 hours. After that,the oxide film was removed, and the mirror-polishing was performed byabout 10 μm thick. Thus processed wafer was used as the active layerside wafer, and a thin-film SOI wafer was fabricated in the smart cutmethod. A condition for the fabrication was as described below.

An oxide film of about 120 nm thick was formed on the active layer sidewafer, and hydrogen ions were implanted in the surface of said wafer.The ion implantation energy was 25 keV and an implantation dose was8×10¹⁶ atoms/cm². After the active layer side wafer having been bondedwith the supporting side wafer, thus obtained bonded wafer washeat-treated at 500° C. for 30 minutes so as to separate a part of theactive layer side wafer from the boundary defined by the minute bubblelayer. Secondly, the bonding strength between the supporting side waferand the active layer was enhanced by the heat treatment at 1100° C. for2 hours. The active layer was thinned ultimately down to 100 nm thickthus to complete the SOI wafer (a sample H). It is to be noted that theseparated active layer side wafer (i.e., the donor wafer) was appliedwith the re-polishing by about 5 μm repeatedly and reused 5 times as theactive layer side wafer. The SOI wafer that had been fabricated at thefifth production cycle was taken as a sample I, on which the defectevaluation was performed along with the sample H.

If any COP representing the void region exists in the active layer sidewafer, there could exist a through hole in the active layer of the SOIwafer. Such holes can be detected in the following manner. That is,firstly the SOI wafer is dipped in hydrofluoric acid. If there exists ahole penetrating through the active layer, during this process ofdipping, the hydrofluoric acid penetrates into that hole, which in turninduces melting of the buried oxide film, and finally it can be detectedeasily with a laser particle counter. The defect to be detected in thismethod (i.e., the hole having penetrated through the active layer) isreferred to as the hydrofluoric acid defect. In the present embodiment,the SOI wafer was dipped in the hydrofluoric acid for 15 minutes, andthe Surfscan 6220 was used to count LPD (Light Point Defect) not smallerthan 5 μm.

The samples H and I were inspected to evaluate the hydrofluoric aciddefect in accordance with the above method, and no defect was detectedfor either of them.

Therefore, it has been found that if the wafer that has been fabricatedin the above-described manner is used as the active layer side wafer, itis possible to fabricate the thin film SOI wafer containing extremelysmall number of hydrofluoric acid defects, and more advantageously ithas been confirmed that the wafer that has been fabricated in the methodof the present invention can be used repeatedly as the active layer sidewafer by performing the polishing in the repeated manner.

Lastly, a wafer to be effectively subject to the heat treatment of thepresent invention will be described. The wafer to be subject thereto isa wafer containing the COP. Whether or not the COP would vanish throughthe oxidizing heat treatment depends on the temperature of the heattreatment and the interstitial oxygen concentration in the wafer but noton the size of the COP.

Accordingly, there is no need to specifically limit the size of the COP.However, since the time required for the heat treatment must be longerfor the larger size of the COP, therefore the smaller size of the COPshould be favorable.

Specifically, the size not greater than 0.2 μm should be substantiallypractical.

The silicon wafer fabricated according to the present invention hasextremely advantageous features that could not be obtained in the methodaccording to the prior art.

(1) The COP has successfully been vanished across a broad range from thesurface to the deep inside of the silicon wafer (e.g., down to the depthof 300 μm).

(2) The specific resistance is highly uniform.

(3) The wafer contains no stacking fault and/or dislocation, which areinherent to the epitaxial wafer.

(4) Since the oxygen concentration is low, there would be an extremelylow possibility in the heat treatment in the device manufacturingprocess that any oxygen composites, such as oxygen precipitates orthermal donor, would be generated, which could vary the specificresistance.

1-19. (canceled)
 20. A manufacturing method of a silicon wafer, in whicha silicon wafer that has been sliced from a silicon single crystal isheat-treated in an oxidizing atmosphere, wherein assuming that atemperature at which said heat treatment is carried out in saidoxidizing atmosphere is denoted as T(° C.) and an interstitial oxygenconcentration is denoted as [Oi] (atoms/cm³), said manufacturing methodof the silicon wafer characterized in that a relation between saidtemperature T and said interstitial oxygen concentration [Oi] satisfiesthe following formula:[Oi]≦2.123×10²¹exp(−1.035/k(T+273)), where, said interstitial oxygenconcentration is a value measured in accordance with FT-IR method (ASTMF-121, 1979) and the k is the Boltzmann's constant, 8.617×10⁻⁵(eV/K).21. A manufacturing method of a silicon wafer in accordance with claim20, in which a single crystal doped with phosphorus by a neutronirradiation is used as said silicon single crystal.
 22. A manufacturingmethod of a silicon wafer in accordance with claim 20, in which a singlecrystal doped with nitrogen by a concentration of 2×10¹³ atoms/cm³ ormore and/or a single crystal doped with carbon by a concentration of5×10¹⁶ atoms/cm³ or more is used as said silicon single crystal.
 23. Amanufacturing method of a silicon wafer in accordance with claim 21, inwhich a single crystal doped with nitrogen by a concentration of 2×10¹³atoms/cm³ or more and/or a single crystal doped with carbon by aconcentration of 5×10¹⁶ atoms/cm³ or more is used as said silicon singlecrystal.
 24. A manufacturing method of a silicon wafer in accordancewith claim 20, in which the silicon wafer is mirror-polished after saidheat treatment in said oxidizing atmosphere.
 25. A manufacturing methodof a silicon wafer in accordance with claim 21, in which the siliconwafer is mirror-polished after said heat treatment in said oxidizingatmosphere.
 26. A manufacturing method of a silicon wafer in accordancewith claim 22, in which the silicon wafer is mirror-polished after saidheat treatment in said oxidizing atmosphere.
 27. A manufacturing methodof a silicon wafer in accordance with claim 23, in which the siliconwafer is mirror-polished after said heat treatment in said oxidizingatmosphere.
 28. A manufacturing method of a SOI wafer, in which a SOIwafer is manufactured by using said silicon wafer manufactured by saidmethod as defined in claim 24 for an active layer side wafer.
 29. Amanufacturing method of a SOI wafer, in which a SOI wafer ismanufactured by using said silicon wafer manufactured by said method asdefined in claim 25 for an active layer side wafer.
 30. A manufacturingmethod of a SOI wafer, in which a SOI wafer is manufactured by usingsaid silicon wafer manufactured by said method as defined in claim 26for an active layer side wafer.
 31. A manufacturing method of a SOIwafer, in which a SOI wafer is manufactured by using said silicon wafermanufactured by said method as defined in claim 27 for an active layerside wafer.
 32. A manufacturing method of a SOI wafer, in which a buriedoxide film is formed by applying a heat treatment to an active layerside silicon wafer in an oxidizing atmosphere, and said active layerside silicon wafer is then bonded to a supporting side wafer with saidburied oxide layer interposed therebetween thus to manufacture a bondedSOI wafer, wherein assuming that a temperature at which said heattreatment is applied to said active layer side silicon wafer in saidoxidizing atmosphere is denoted as T(° C.) and an interstitial oxygenconcentration of said active layer side silicon wafer is denoted as [Oi](atoms/cm³), said manufacturing method of the SOI wafer characterized inthat a relation between said heat treatment temperature T and saidinterstitial oxygen concentration [Oi] of said active layer side siliconwafer satisfies the following formula:[Oi]≦2.123×10²¹exp(−1.035/k(T+273)), where, said interstitial oxygenconcentration is a value measured in accordance with FT-IR method (ASTMF-121, 1979) and the k is the Boltzmann's constant, 8.617×10⁻⁵(eV/K).33. A manufacturing method of a SOI wafer in accordance with claim 32,in which said active layer side silicon wafer is fabricated by using asilicon single crystal doped with phosphorus by neutron irradiation. 34.A manufacturing method of a SOI wafer in accordance with claim 32, inwhich said active layer side silicon wafer is fabricated by using asilicon single crystal doped with nitrogen by a concentration of 2×10¹³atoms/cm³ of more and/or by using a silicon single crystal doped withcarbon by a concentration of 5×10¹⁶ atoms/cm³ or more.
 35. Amanufacturing method of a SOI wafer in accordance with claim 33, inwhich said active layer side silicon wafer is fabricated by using asilicon single crystal doped with nitrogen by a concentration of 2×10¹³atoms/cm³ of more and/or by using a silicon single crystal doped withcarbon by a concentration of 5×10¹⁶ atoms/cm³ or more.
 36. Amanufacturing method of a SOI wafer, in which an active layer sidesilicon wafer is bonded to a supporting side wafer with an insulatingfilm interposed therebetween and then a heat treatment for enhancing abonding strength is applied to thus bonded wafer in an oxidizingatmosphere to thereby manufacture a bonded SOI wafer, wherein assumingthat a temperature at which said heat treatment for enhancing thebonding strength is carried out in said oxidizing atmosphere is denotedas T(° C.) and an interstitial oxygen concentration of said active layerside silicon wafer is denoted as [Oi] (atoms/cm³), said manufacturingmethod of the SOI wafer characterized in that a relation between saidtemperature T and said interstitial oxygen concentration [Oi] satisfiesthe following formula:[Oi]≦2.123×10²¹exp(−1.035/k(T+273)), where, said interstitial oxygenconcentration is a value measured in accordance with FT-IR method (ASTMF-121, 1979) and the k is the Boltzmann's constant, 8.617×10⁻⁵ (eV/K).37. A manufacturing method of a SOI wafer in accordance with claim 36,in which said active layer side silicon wafer is fabricated by using asilicon single crystal doped with phosphorus by neutron irradiation. 38.A manufacturing method of a SOI wafer in accordance with claim 36, inwhich said active layer side silicon wafer is fabricated by using asilicon single crystal doped with nitrogen by a concentration of 2×10¹³atoms/cm³ or more and/or by using a silicon single crystal doped withcarbon by a concentration of 5×10¹⁶ atoms/cm³ or more.
 39. Amanufacturing method of a SOI wafer in accordance with claim 37, inwhich said active layer side silicon wafer is fabricated by using asilicon single crystal doped with nitrogen by a concentration of 2×10¹³atoms/cm³ or more and/or by using a silicon single crystal doped withcarbon by a concentration of 5×10¹⁶ atoms/cm³ or more.
 40. Amanufacturing method of a SOI wafer, comprising the steps of:fabricating an active layer side silicon wafer by firstly applying anoxidizing heat treatment to a silicon wafer, which satisfies thefollowing formula representing a relation between a heat treatmenttemperature T and an interstitial oxygen concentration [Oi]:[Oi]≦2.123×10²¹exp(−1.035/k(T+273)), where, T(° C.) is the temperatureat which said heat treatment is carried out in an oxidizing atmosphere,and [Oi] (atoms/cm³) is the interstitial oxygen concentration in thesilicon wafer, wherein said interstitial oxygen concentration is a valuemeasured in accordance with FT-IR method (ASTM F-121, 1979) and the k isthe Boltzmann's constant, 8.617×10⁻⁵ (eV/K), and by secondly removing anoxide film and applying a mirror-polishing; forming an ion implantedlayer in said active layer side silicon wafer by forming an oxide filmon said active layer side silicon wafer, and ion-implanting via saidoxide film; subsequently, forming a bonded wafer by bonding said activelayer side silicon wafer to a supporting side wafer with said oxide filminterposed therebetween; and then, separating a part of said activelayer side silicon wafer from a boundary defined by said ion implantedlayer by holding said bonded wafer at a predetermined temperature tothereby apply a heat treatment thereto.
 41. A manufacturing method of aSOI wafer in accordance with claim 40, in which a surface of theseparated active layer side wafer is mirror-polished so that it can beused repeatedly as a substrate for forming a new active layer of the SOIwafer.
 42. A manufacturing method of a SOI wafer in accordance withclaim 40, in which said active layer side silicon wafer is fabricated byusing a silicon single crystal doped with phosphorus by neutronirradiation.
 43. A manufacturing method of a SOI wafer in accordancewith claim 41, in which said active layer side silicon wafer isfabricated by using a silicon single crystal doped with phosphorus byneutron irradiation.
 44. A manufacturing method of a SOI wafer inaccordance with claim 40, in which said active layer side silicon waferis fabricated by using a silicon single crystal doped with nitrogen by aconcentration of 2×10¹³ atoms/cm³ or more and/or by using a siliconsingle crystal doped with carbon by a concentration of 5×10¹⁶ atoms/cm³or more.
 45. A manufacturing method of a SOI wafer in accordance withclaim 41, in which said active layer side silicon wafer is fabricated byusing a silicon single crystal doped with nitrogen by a concentration of2×10¹³ atoms/cm³ or more and/or by using a silicon single crystal dopedwith carbon by a concentration of 5×10¹⁶ atoms/cm³ or more.
 46. Amanufacturing method of a SOI wafer in accordance with claim 42, inwhich said active layer side silicon wafer is fabricated by using asilicon single crystal doped with nitrogen by a concentration of 2×10¹³atoms/cm³ or more and/or by using a silicon single crystal doped withcarbon by a concentration of 5×10¹⁶ atoms/cm³ or more.
 47. Amanufacturing method of a SOI wafer in accordance with claim 43, inwhich said active layer side silicon wafer is fabricated by using asilicon single crystal doped with nitrogen by a concentration of 2×10¹³atoms/cm³ or more and/or by using a silicon single crystal doped withcarbon by a concentration of 5×10¹⁶ atoms/cm³ or more.